Newcastle's 12-10 victory over the Warriors at Auckland's Eden Park has earned the Knights a preliminary-final meeting with Penrith.
Fletcher Sharpe and Dominic Young scored for Newcastle, which was missing several key players and faced a strongly pro-Warriors crowd.
The Knights will play the Panthers at Accor Stadium on Sunday in their first preliminary final since 2013.
Captain Kalyn Ponga passed his head injury assessment after leaving late in the match, clearing him to play.
"I'm really proud of the boys, there's a lot of young lads out there and this is their first time in front of 50,000 plus," Ponga said.
Newcastle's revival under Justin Holbrook follows last year's wooden spoon and includes away finals victories against South Sydney and the Warriors.
The result was clouded by late officiating disputes and reports that spectators threw projectiles towards referee Ashley Klein.
Warriors forward Te Maire Martin was penalised for stripping the ball, while Klein did not penalise Tyson Frizell for appearing to impede Leka Halasima.
Warriors coach Andrew Webster said the decision could have enabled a two-point attempt to force golden point.
"I thought they were trying to find ways to take it off us," Webster said.
Halasima scored twice, including in the 70th minute, but Taine Tuaupiki missed the conversion from the sideline.
Newcastle held firm through the closing pressure, while the Warriors ended the finals in straight sets after narrowly missing the minor premiership.
"We've got a lot of confidence in ourselves and self belief and whoever we're playing, we play well and we know we can win," Holbrook said.